Present methods for electron capture detection require sample injections restricted to approximately 5 p1 or less to avoid the possibility of detecting solvents or other source contaminants, interferences from carrier vehicles, e.g., blood, serum, and sewage. With the LC-UV method, many of these problems are avoided because of the specificity of UV. An example is given in the less stringent requirements for the solvents used. This technique can serve as a complementary method to GC-EC, achieving a comparable range of sensitivity. The UV detector was found to be very reproducible, requiring much less time for stabilization. The cleanup procedures for HCP extracted from blood serum, or other body fluids (3,4,8,9) are good starting points for specific problems. The authors have not made any extensive studies on the suitability of this approach to the various cleanup methods referred to. However, it is interesting to postulate. In the case of HCP added to and recovered as described (2, 8), approximately 0.03 ppm was found to be the lowest detectable range. Although calibrations are presented by LC with lower limits of 40 ng detectable per 10-111 injections, it becomes possible with the larger 20-111 injections permissible and after suitable concentrating, to detect at the 0.03-ppm level also. If, as an example, 100 ng of HCP were added to 3 ml of blood, the level would be 0.033 ppm or 33 ppb. After suitable cleanup, using the method described (8) as a guide, assume this amount is isolated and exists in a dry residue. It can then be derivatized as described, the caution being to allow the anisoyl
Table I. Dianisate Derivatization of HCP Anisoyl Conversion, chloride, pl HCP, pg Time, min 10 10 10 77.1 10 10 20 77.1 10 10 30 76.0 20 10 20 89.2 30 10 20 99.0
z
chloride reagent to contact HCP without interference from residual fatty materials acting as a barrier when the diester hexane extraction is evaporated to dryness. One hundred microliters of n-butylchloride can be used for solution. This volume will contain a stoichiometric amount of HCP-DA, which in this case is 166 ng. A 2 0 4 aliquot injection will contain 33 ng. Therefore, the original 100 ng of HCP added to 3 ml of blood is ultimately detected as 33 ng of HCP-DA in 20 pl of butylchloride. This novel approach is presented to those actively engaged in similar work to evaluate as an alternate detection method. It demonstrates once again the broad capabilities and utility of LC as a complement to GC. ACKNOWLEDGMENT
The authors express their appreciation for the cooperation and helpful suggestions given by Julian Dorsky and Gary Shaffer and to Axel Kiesslich, who contributed much to the LC work.
(8) P. J. Porcaro, P. Shubiak, and M. Manowitz, J. Pharm. Sci., 58, 251 (1969). (9) R. C. Bachman and M. R. Shetler, Biochem. Med., 2, 313 (1969).
RECEIVED for review February 23, 1972. Accepted May 1, 1972.
Hamming Type Codes Applied to Learning Machine Determinations of Molecular Formulas F. E. Lytle Department of Chemistry, Purdue University, Lafayette, Ind. 47907
MOSTOF THE CURRENT CHEMICAL RESEARCH involving machine intelligence has been devoted to new data base applications and faster or more reliable training procedures ( I ) . In contrast, relatively little attention has been paid to the problem of class construction with respect to both minimizing the number of necessary threshold logic units (TLU’s) and maximizing their reliability. The purpose of this communication is to demonstrate how arrays of TLU’s might be constructed so as to introduce a degree of redundancy into the decision making process. In particular, it is shown theoretically, how Hamming type self-correcting error codes can improve classification schemes used for the determination of molecular formulas. The proposed method can not only detect the fact that an error has been made in the overall procedure, but can also indicate which TLU was wrong and in what direction!
RESULTS AND DISCUSSION
Assume for the sake of discussion that the molecular formula questions asked of the machine involve carbon number, with the only possibilities being zero through fifteen. Historically, two approaches have been used. The first one might be called the “linear” method. Sixteen TLU’s are trained, corresponding to all possible carbon numbers. This scheme proceeds as follows: /Ta(l) = {Co] uO\T~(0) = {CI,CS,C3. , , .c14, C I ~ ]
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/ T P ( ~=) (CIS,C14, c13, CIZ,C7, C6, CS,C4} = {GI,G O ,Cg, Cs, ca, CP,C1, CO)
Table I. TLU Outputs for a Carbon Number of Ten (a) The Binary Method
u2\TP(O)
T3(1) = (Clb c14, c 1 3 7 c12, c11, c10, c9, CE) = { c7, c6, c5, c4, c3, CZ, c1, CO}
(U3U2UlUOJ = { 1 0 1 0 )
u 3
